Recessed lighting fixtures are versatile and popular for a variety of indoor and outdoor illumination applications and are widely used for general illumination, architectural lighting, accent lighting, task lighting and underwater lighting. Their popularity stems in large measure from the fact that in addition to being able to provide a level of illumination appropriate to a particular application, the bulk of a recessed fixture is concealed in or behind the recess in which it is mounted. As such, they are unobtrusive, occupy little or no space in the area being illuminated, and can cast light outward from behind, flush with, or close to a surface so that substantially the entire region forward of the surface can be lighted.
Recessed lighting fixtures have two main parts, which are typically referred to in the lighting industry as the “trim” and the “housing”. The housing is the portion that is installed in a recess which at least partially penetrates a wall, ceiling, stair riser, bollard or other architectural structure. Typically, all or most of the housing is substantially concealed within the recess by the trim after the fixture has been installed.
The trim is generally the part of a recessed fixture that is most visible after the fixture has been installed in a recess opening and it often has a decorative appearance. Trim can be highly ornamented or of an unobtrusive style that is intended to blend in with its surroundings in an understated manner. In recessed ceiling-mounted fixtures for example, the trim often takes the form of a low-profile ring having an aperture in the middle from which the illumination emanates. The aperture can simply be an uncovered opening or, it can be fitted with a transparent or translucent cover known as a “lens”. As used in the lighting industry, the term “lens” can encompass, but is not limited to, an element that focuses, de-focuses or re-directs light and/or one that has an axis of symmetry.
In addition to holding the illumination source or “lamp”, an important function of the housing of a conventional recessed lighting fixture is to safely dissipate enough of the heat given off by the lamp to prevent a fire hazard. Although it is common to also include a thermal safety switch as backup protection recess, mounted lighting fixtures generally depend heavily on direct convective exchange between the exterior ambient environment and spaces inside and/or around the recessed portion of the housing in order to keep the temperature of the components of the fixture within safe and otherwise acceptable limits.
In the case of a recessed indoor ceiling-mounted lighting fixture, the recess opening is usually a hole which completely penetrates the ceiling drywall and the housing mounts mostly above the hole in the space above drywall. In the United States, housings for those types of fixtures are classified as either “IC” or “Non-IC”. Type IC (for “insulation contact”) housings are primarily used for new construction housings and are generally fastened to the ceiling joists before the drywall or other ceiling material is installed. Building codes allow IC housings to directly contact building insulation material but are typically rated for use with lamps of not more than about seventy five watts (75 W).
Non-IC rated housings can be rated to safely accommodate lamps of up to about one hundred fifty watts (150 W) but can be used in compliance with most building codes only if a minimum spacing of about three inches or more is present on all sides between the housing and any insulation. Recessed lighting fixtures with non-IC rated housings can be installed before installation of the ceiling panel but are also available in configurations which can be installed by passing the housing through a hole cut in the ceiling and are ideal for retrofit applications in a ceiling.
In other applications, such as recessed light fixture or luminaire to be mounted in a recess in a bollard, pool, fountain, garden wall, or stair riser of an outdoor stairway, the recess opening typically does not completely penetrate the structure but instead terminates so that the recess takes the form of a niche which is closed-off on all but one side. Such applications can be particularly challenging, even with fixtures using conventional lamps, since little free space or convective circulation may be available within the confines of the niche to adequately cool the fixture. They are made even more difficult if one wishes to meet the needs of applications in which it would not be possible, or would be undesirable, to provide the trim with vents capable of permitting substantial convective flow to take place through the aperture or other parts of the trim, to transfer heat by convection from the housing to the ambient environment which interfaces with the exterior of the trim. They are made more challenging still if one wishes to address such applications while at the same time providing energy savings which are offered by using energy efficient light emitting diodes as a light source rather than an incandescent bulb or other conventional lamp.
Conventional incandescent bulbs produce light by passing an electric current through a thin filament which is heated by the current until it glows brightly. LED's produce light by a completely different mechanism. An LED is a semiconductor device, namely a diode junction between a p-type semiconductor material and n-type semiconductor material. As an electric current is passed in the forward direction across the p-n junction of an LED, photons are given off as electrons making up the flow of current change their energy levels, thus producing light. This process, called electroluminescence, is an efficient way of generating light from electricity, particularly in comparison to incandescent bulbs and many other types of lamps. However, it is not a process which results in 100% conversion of electrical energy into light. A significant fraction of the energy represented by the electric current flowing through an LED generates heat rather than light. If sufficient amounts of heat are not carried away from the area of the p-n junction at a sufficient rate, it will cause the operating temperature of the LED to rise to an unacceptably high temperature which could cause the LED to fail prematurely. Thus, unlike incandescent bulbs and certain other technologies such as high intensity discharge (HID) lamps, which not only tolerate but require extreme temperatures in order to generate light, LED's are relatively intolerant of high temperatures, particularly if one desires to maximize the operating life if the LED.
In order to carry away enough heat, light fixtures and luminaires for general and architectural illumination using LED's typically rely at least in part on convection in the immediate vicinity the LED to help carry away enough the excess heat generated by the LED. However, in the case of recessed lighting in particular, designers and architects cannot always rely on there being sufficient space and/or ventilation available in the recessed area behind the trim of the fixture where the LED is located. For example, there may be thermal insulation present in the area behind the recess opening which impedes convective flow as well as conduction of heat from the recessed portion of the fixture. To compensate for this, the trim is typically provided with one or more vent openings that allow convection currents to pass through the trim to cool the lamp and other areas behind the inside surface of the trim. In many cases, such vent openings consist of or include the aperture in the trim through which the illumination is delivered. However, it is not always possible or desirable to provide vent openings through or behind the trim of a recessed fixture or luminaire. For example, in certain wet or underwater applications, it may be necessary or desirable to seal off the trim and/or at least the LED, to isolate internal components from environment which adjoins the outside surface of the trim in order to provide such components with mechanical protection and/or prevent the intrusion of water into them. Such constraints on heat removal have resulted in limitations as to either or both: (i) the degree to which fixtures and luminaires of this type can be effectively sealed against intrusion of fluids and/or (ii) their total maximum wattage and thus, the amount of light they can provide.